Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Also, Functional Electrical Stimulation (FES) systems such as the Freehand system by NeuroControl (Cleveland, Ohio) have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Each of these implantable neurostimulation systems typically includes one or more stimulation leads implanted at the desired stimulation site. In the context of an SCS procedure, one or more stimulation leads are introduced through the patient's back into the epidural space under fluoroscopy, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array.
The specific procedure used to implant the stimulation leads in an SCS procedure will ultimately depend on the type of stimulation leads used. Currently, there are two types of commercially available stimulation leads: a percutaneous lead and a surgical lead.
A percutaneous lead comprises a cylindrical body with ring electrodes, and can be introduced into contact with the affected spinal tissue through a Touhy-like needle, which passes through the skin, between the desired vertebrae, and into the epidural space above the dura layer. For unilateral pain, a percutaneous lead is placed on the corresponding lateral side of the spinal cord. For bilateral pain, a percutaneous lead is placed down the midline of the spinal cord, or two percutaneous leads are placed down the respective sides of the midline. In many cases, a stylet, such as a metallic wire, is inserted into a lumen running through the center of each of the percutaneous leads to aid in insertion of the lead through the needle and into the epidural space. The stylet gives the lead rigidity during positioning, and once the lead is positioned, the stylet can be removed after which the lead becomes flaccid.
A surgical lead has a paddle on which multiple electrodes are arranged in independent columns, and is introduced into contact with the affected spinal tissue using a surgical procedure, and specifically, a laminectomy, which involves removal of the laminar vertebral tissue to allow both access to the dura layer and positioning of the lead.
Each of the above-mentioned implantable neurostimulation systems also comprises an implantable neurostimulator, such as an implantable pulse generator (IPG), implanted remotely from the stimulation site, but coupled to the stimulation leads. Thus, electrical pulses can be delivered from the neurostimulator to the stimulation leads to stimulate the tissue and provide the desired efficacious therapy to the patient. In the context of an SCS procedure, the electrical pulses are delivered to the dorsal column and dorsal root fibers within the spinal cord. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient.
Each stimulation lead may be directly coupled to the neurostimulator or indirectly coupled to the neurostimulator via an extension leads in cases where the length of the stimulation leads is insufficient to reach the neurostimulator.
If the stimulation leads are to be directly connected to the neurostimulator, the proximal ends of the stimulation leads can be inserted into a connector of the neurostimulator (via connector ports located on a header of the neurostimulator), such that the terminals located at the proximal ends of the stimulation leads are coupled to corresponding electrical contacts within the connector. Individual wires are routed though lumens in each stimulation lead to connect the proximally-located terminals with the distally-located electrodes.
If the stimulation leads are to be indirectly connected to the neurostimulator via the extension leads, the proximal ends of the stimulation leads can be inserted into connectors located at the distal ends of the respective extension leads, such that the terminals of the stimulation leads are coupled to corresponding electrical contacts within the connectors of the extension leads. The proximal ends of the extension leads can then be inserted into the connector of the neurostimulator, such that terminals located at the proximal ends of the extension leads are coupled to the corresponding electrical contacts within the connector of the neurostimulator. Individual wires are routed though lumens in each extension lead to respectively couple the proximally-located terminals to the distally-located electrical contacts.
After the system is fully implanted, it is important that the subcutaneously implanted components, such as the neurostimulator and extension leads, be of a low-profile nature for aesthetic reasons as well as to prevent or minimize any discomfort of the patient that may otherwise occur by having rigid objects that do not conform to the natural curvature and movement of the patient.
However, in order to accommodate the present-day contacts, which either take the form of metal collars containing set screws or Bal-Seal® contacts composed of springs contained within steel ring housings, the connectors of the extension lead and adapter are typically larger and stiffer than the bodies of the extension lead and adapter, thereby increasing the overall profile, while decreasing the conformity, of the extension lead and adapter. In addition, Bal-Seal® contacts are also relatively expensive, which given the number of contacts required, may result in a connector that is prohibitively expensive. Furthermore, metal collars for accommodating screws and the spring coil within the Bal-Seal® contacts are relatively long, thereby limiting the number of contacts that can be incorporated into a connector. Although the current connector designs can accommodate up to eight Bal-Seal® contacts, future connector designs will need to accommodate more contacts (e.g., 12-16). However, in order to accomplish this using Bal-Seal® contacts, the length of the connector would have to be increased, which may be unacceptable.
There, thus, remains a need for a lower-profile, high resolution connector for an electrical lead assembly.